1. Field of the Invention
This invention relates to phenylcyclohexyldioxane derivatives having an ether bond which are useful as an electro-optical display material.
2. Prior Art
Representative examples of liquid crystal display devices include field-effect mode proposed by M. Schadt, et al., (APPLIED PHYSICS LETTERS, 18, 127-128 (1971)); dynamic scattering mode proposed by G. H. Heilmeier, et al., (PROCEEDING OF THE I.E.E.E., 56, 1162-1171 (1968)); and guest host mode proposed by G. H. Heilmeier, et al., (APPLIED PHYSICS LETTERS, 13, 91 (1968)), or by D. L. White, et al , (JOURNAL OF APPLIED PHYSICS, 45. 4718 (1974)).
Among these types of liquid crystal display devices (LCDs), the twisted nematic liquid crystal display devices (TN-LCDs) which fall in the group of the field-effect mode cells currently are of greatest interest.
As reported by G. Bauer (Mol. Cryst. Liq. Cryst. 63, 45 (1981)), in the TN-LCDs, the product of the anisotropy, .DELTA.n, of refractive index of a liquid crystal material to be filled in a cell, and the thickness d (in .mu.m) of the liquid crystal layer in the cell must be set to a specified value in order to prevent the occurrence of interference fringes on the surface of the cell, which could impair the appearance of the cell. In cells in practical use, the value of .DELTA.n.d is set to one of 0.5, 1.0, 1.6 or 2.2. Usually, such cells have a feature that when the value of .DELTA.n.d is set to 0.5, the visual appearance of the cell is improved, whereas when the value is set to 1.0, 1.6 or 2.2, the contrast of the cell viewed from the front is improved. Therefore, it is usual practice that in the case of liquid crystal display cells in which primary importance is placed on the visual characteristic that the cell be easily visible from all viewing angles, the value of .DELTA.n.d is set to 0.5; whereas in the case of liquid crystal display cells in which primary importance is attached to the contrast of cells viewed from the front, the value of .DELTA.n.d is set to 1.0, 1.6, or 2.2.
On the other hand, the thickness d of the liquid crystal layer in liquid crystal display cells in practical use is usually set to a value within the range of 6 to 10 .mu.m, and hence when the value of .DELTA.n.d is set to 0.5, liquid crystal material having a small value of .DELTA.n is required; whereas when the value of .DELTA.n.d is set to 1.0, 1.6, or 2.2, a liquid crystal material having a large value of .DELTA.n must be used. As stated above, a liquid crystal material having a small or large value of .DELTA.n becomes necessary depending on which display characteristics are desired in the liquid crystal display cells.